Talk:G-value

Are there any references as to where these the two definintions for G-value originate? Bewp 11:07, 11 June 2007 (UTC) SHGC is Solar Heat Gain ? as defined by ASHRAE whereas g value is the same thing almost as defined by Euro Norm EN 13363-1 Oct 2003. There needs to be a cross reference between SHGC and g value. Then there needs to be a clear exposition of both so that the principals and the details can be understood and any differences picked out. The general remarks stated below are broadly correct, but it would be good to have a more rigorous discussion.[Max Fordham 10 Dec 2007] Max Fordham (talk) 19:29, 10 December 2007 (UTC) There is confusion on G-value and SHGC.

Many people think SHG is caused only by IR and UV.

But, for G-value, it talks about solar radiation (including visible light).

So does G-value = SHGC?

What is SHGC? (transmitted IR+UV)/ (total IR + UV), or (transmitted IR+visible+UV)/ (total IR+Visible+UV)

Who knows?

I'm not very well-versed in G-value so I can't say for sure whether or not it is synonymous with SHGC. However, what SHGC is, is (in essence):

Transmitted solar radiation (UV, IR and Visible Light) + Re-radiated Solar radiation (UV, IR and Visible Light)

[Value between 0 and 1]

So SHGC does include Visible Light, but it also takes into account Re-radiated energy, not just transmitted. This Re-radiated energy is a portion of the Total solar radiation (UV, IR and Visible Light) Absorbed. The portion is taken by convention to be 27% thereabouts (based on certain assumptions). So, is this similar to G-value? Someone? Anyone? NVX 06:47, 14 August 2007 (UTC)